Components with relatively complex three-dimensional (3D) geometries raise difficult fabrication issues. Conventional fabrication techniques include forging, casting, and/or machining. Such conventional methods are not only expensive and have long lead-times, but may additionally have low yields. Development time and cost for certain components may also be magnified because such components generally require several iterations, including iterations as a result of intentional design decisions.
Additive manufacturing (AM) processes (including those which form “cores” for subsequent conventional casting) have been developed to fabricate components having relatively complex three dimensional geometries, including components with internal surfaces defining internal passages including internal hollow areas, internal channels, internal openings or the like (collectively referred to herein as “internal passages”) for cooling, weight reduction, or otherwise. Additive Manufacturing (AM) is defined by the American Society for Testing and Materials (ASTM) as the “process of joining materials to make objects from 3D model data, usually layer upon layer, as opposed to subtractive manufacturing methodologies, such as traditional machining and casting.” In an additive-manufacturing process, a model, such as a design model, of the component may be defined in any suitable manner. For example, the model may be designed with computer aided design (CAD) software. The model may include 3D numeric coordinates of the entire configuration of the component including both external and internal surfaces. The model may include a number of successive 2D cross-sectional slices that together form the 3D component.
Components manufactured from additive manufacturing processes may have significant surface roughness, surface porosity and cracks (hereinafter “surface-connected defects”), and internal porosity and cracks (hereinafter “internal defects”). The term “internal defects” also includes bond failures and cracks at the interfaces between successive cross-sectional deposit layers. Cracks may develop at these interfaces or cut through or across deposit layers dues to stresses inherent with the additive manufacturing process and/or the metallurgy of the build material.
A hot isostatic pressing (HIP) process may be used to eliminate internal defects but not the surface-connected defects. For components needing HIP because of the presence of internal defects, an encapsulation process may be used to bridge and cover the surface-connected defects, effectively converting the surface-connected defects into internal defects in preparation for subsequent hot isostatic pressing (HIP) processing. However, for components with significant surface roughness, the encapsulation process may not sufficiently bridge and cover the surface-connected defects. Surface roughness may also be objectionable to customer perception of quality and may interfere with the functionality of the component. For example, excessive surface roughness may restrict or impede airflow, collect debris, act as a stress riser, and otherwise detract from the component design.
Unfortunately, the reduction of internal passage surface roughness presents a particular manufacturing challenge because of the general inaccessibility of the internal passage surfaces. Conventional polishing or milling techniques to reduce internal passage surface roughness are not as developed as they are for external surfaces. No effective process exists to uniformly reduce internal passage surface roughness to acceptable levels, thereby compromising the structural integrity, cosmetic appearance, functionality, and mechanical properties of the component, and also not allowing the encapsulation process to sufficiently bridge and cover the surface-connected defects in preparation for HIP processing. Even with encapsulation, faying surfaces of some surface-connected defects may not be sufficiently metallurgically diffusion bonded if excessively oxidized or otherwise insufficiently cleaned. A component with inadequate diffusion bonded surfaces has a compromised metallurgical surface integrity that reduces the overall metallurgical quality of the manufactured component.
Accordingly, it is desirable to provide methods for manufacturing components from articles formed by additive-manufacturing processes. It is also desirable to provide methods that uniformly reduce surface roughness, including internal passage surface roughness, thereby improving the structural integrity, cosmetic appearance, functionality, mechanical properties, and fatigue life/strength of the component, that allow encapsulation of the additive-manufactured article to be effective in preparation for subsequent hot isostatic pressing (HIP) processing, and that improve metallurgical quality of the component. It is also desirable to provide methods for manufacturing components that improve yield, enable improved development cycle times and reduced tooling costs without sacrificing component performance or durability, enable multiple design iterations at relatively low cost and short delivery times, and permit internal configurations for components not otherwise possible with current casting technology. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.